multicopter land detector: make threshold for _has_low_thrust

src/modules/land_detector/MulticopterLandDetector.cpp

@@ -82,6 +82,7 @@ MulticopterLandDetector::MulticopterLandDetector()
 	_paramHandle.freefall_trigger_time = param_find("LNDMC_FFALL_TTRI");
 	_paramHandle.altitude_max = param_find("LNDMC_ALT_MAX");
 	_paramHandle.landSpeed = param_find("MPC_LAND_SPEED");
+	_paramHandle.low_thrust_threshold = param_find("LNDMC_LOW_T_THR");
 
 	// Use Trigger time when transitioning from in-air (false) to landed (true) / ground contact (true).
 	_landed_hysteresis.set_hysteresis_time_from(false, LAND_DETECTOR_TRIGGER_TIME_US);
@@ -126,6 +127,8 @@ void MulticopterLandDetector::_update_params()
 	_freefall_hysteresis.set_hysteresis_time_from(false, (hrt_abstime)(1e6f * _params.freefall_trigger_time));
 	param_get(_paramHandle.altitude_max, &_params.altitude_max);
 	param_get(_paramHandle.landSpeed, &_params.landSpeed);
+	param_get(_paramHandle.low_thrust_threshold, &_params.low_thrust_threshold);
+
 }
 
 
@@ -314,7 +317,8 @@ bool MulticopterLandDetector::_is_climb_rate_enabled()
 bool MulticopterLandDetector::_has_low_thrust()
 {
 	// 30% of throttle range between min and hover
-	float sys_min_throttle = _params.minThrottle + (_params.hoverThrottle - _params.minThrottle) * 0.3f;
+	float sys_min_throttle = _params.minThrottle + (_params.hoverThrottle - _params.minThrottle) *
+				 _params.low_thrust_threshold;
 
 	// Check if thrust output is less than the minimum auto throttle param.
 	return _actuators.control[actuator_controls_s::INDEX_THROTTLE] <= sys_min_throttle;

src/modules/land_detector/MulticopterLandDetector.h

@@ -107,6 +107,7 @@ class MulticopterLandDetector : public LandDetector
 		param_t freefall_trigger_time;
 		param_t altitude_max;
 		param_t landSpeed;
+		param_t low_thrust_threshold;
 	} _paramHandle{};
 
 	struct {
@@ -120,6 +121,7 @@ class MulticopterLandDetector : public LandDetector
 		float freefall_trigger_time;
 		float altitude_max;
 		float landSpeed;
+		float low_thrust_threshold;
 	} _params{};
 
 	int _vehicleLocalPositionSub{ -1};

src/modules/land_detector/land_detector_params_mc.c

@@ -113,3 +113,21 @@ PARAM_DEFINE_FLOAT(LNDMC_FFALL_TTRI, 0.3);
  *
  */
 PARAM_DEFINE_FLOAT(LNDMC_ALT_MAX, -1.0f);
+
+/**
+ * Low throttle detection threshold.
+ *
+ * Defines the commanded throttle value below which the land detector
+ * considers the vehicle to have "low thrust". This is one condition that
+ * is used to detect the ground contact state. The value is calculated as
+ * val = (MPC_THR_HOVER - MPC_THR_MIN) * LNDMC_LOW_T_THR + MPC_THR_MIN
+ * Increase this value if the system takes long time to detect landing.
+ *
+ * @unit norm
+ * @min 0.1
+ * @max 0.9
+ * @decimal 2
+ * @group Land Detector
+ *
+ */
+PARAM_DEFINE_FLOAT(LNDMC_LOW_T_THR, 0.3);